IR STUDY OF TIO2-BASED GAS-SENSOR MATERIALS - EFFECT OF RUTHENIUM ON THE OXIDATION OF NH3, (CH3)3N AND NO

The adsorption and oxidation of ammonia, trimethylamine and nitric oxide on Ru/TiO2 and TiO2 have been studied by FTIR spectroscopy. On both the samples ammonia and trimethylamine are adsorbed at room temperature molecularly on the surface Ti4+ sites. By heating ammonia at T>473 K, water and hydroxyls are produced. The oxidation at 473 K of the trimethylamine on both the samples leads to the formation of dimethylformamide and water; the oxidation at T>573 K on pure TiO2 leaves residual NH and CH(x) groups; on Ru/TiO2 a complete oxidation occurs, leading to nitrosyl species adsorbed on Ru ions and to nitrate species and water on titania. NO adsorbs molecularly on oxidized Ru/TiO2 samples, with formation of Ru3+-NO surface complexes; on the contrary it does not adsorb at all as such on pure TiO2. On both the samples, nitrate species on titania are produced by interaction with dry air. The complex of data presented in the paper indicates that the presence of the Ru as a metallic activator allows a more complete oxidation of the studied molecules, justifying the higher sensitivity.